The present invention relates to wound dressings and methods for the preparation thereof. More specifically, the present invention relates to a method for preparing dressings for treating pyo-necrotic and infected wounds, topical ulcers and for prophilaxis of suppuration of infected wounds.
It is known in medical practice to use native proteolytic enzyme preparations for treating pyo-inflammatory diseases. However, said enzymes are expensive and scarce. Regardless of certain effectiveness, said enzymes are not resistant against inhibitors which are contained in wound discharge, or against pH and temperature changes. During release of native enzymes into wound exudates, said enzymes are quickly inactivated, therefore treatment requires a considerable amount of enzymes.
For reduction of the need for enzymes, a dressing was created which has a prolonged action, contains immobilized enzymes on textile material and is resistant to environmental influence, but has a lower therapeutically activity than the activity of native enzymes.
A method is known in the art for preparing a material having immobilized enzymes which comprises the following steps:
Activating the textile carrier by introducing functional groups into the carrier until the amount of reactive functional groups reaches 0.0625-3.125 mg-equiv. of reactive functional groups per gram of a carrier.
Treating the activated carrier with a solution of enzymes in buffer solutions having a pH of 6.5-7.5 at room temperature for 8-16 hours; and washing and drying the active textile carrier.
Materials having a biological activity and having a prolonged action have been prepared by said method with an immobilized enzyme. Said material is used for treating wounds and burns (laid-open German Patent No. 4000797, C 12N 11/02, Jul. 18, 1991).
Said method is disadvantageous in that the enzyme activity is reduced with its chemical immobilization. It results in producing a dressing having lower therapeutical effectiveness in comparison with native enzyme.
Similarly, known in the art is a method for preparing a material having immobilized enzyme, which comprises the following steps:
activating the textile carrier;
treating the carrier with solution of trypsin (0.05%) in a phosphate buffer having a pH of 6.5-6.7 at module of 5-6 for 2 hours; and
the obtained cloth is squeezed out, dried and treated by solution of insulin having an activity of 4.0-4.4 units per ml (Russian Patent No. 2062113, A 61 L 15/38, Jun. 20, 1996.
The materials prepared by said method produce a long necrolytic, anti-inflammatory, anti-toxic and draining effect, but the method for preparing the material is time consuming and the obtained cloth has a lower therapeutical effectiveness of native enzyme.
Similarly known in the art is a method for the preparation of a material containing immobilized enzyme which comprises the following steps:
activating the textile carrier by forming therein reactive functional groups containing 0.5% w/w (corresponds to 0.0625 mg-eq. of aldehyde per gram of carrier)xe2x80x94to 25% w/w (corresponds to 3.125 mg-eq. of aldehyde per gram of carrier).
treating the carrier with a trypsin solution, 0.02%-0.05% w/w in a phosphate buffer, pH 6.5-7.5 at room temperature for 8-16 hours in order to form a covalent bond between the activated carrier, i.e., the oxidized textile, and the enzyme.
The cloth is then squeezed and washed with water until no biological activity can be detected, and dried at room temperature (GB PATENT No. 2,240,040 A, Dated Jul. 24, 1991.
The materials prepared by said method have necrolytic, anti-inflammatory, anti-toxic and draining properties, but the preparation method is time consuming, effective for 4 days (only mentioned but even not claimed), and have a lower therapeutical effectiveness than the native enzyme. These activity duration and effectiveness are obtained by incorporating into the textile fabric a relatively high amount of functional groups: 0.5% w/w to 25% w/w as aforesaid.
Due to the high amount of functional groups and as a result of the binding nature of the immobilized enzyme(s) to the activated cloth, a relatively high amount of the immobilized enzyme is bound. The lower therapeutical effectiveness of the cloth, despite the relatively high amount of enzyme(s) incorporated, is a result of the binding nature of the immobilized enzyme(s) as described and explained herein.
The bonding nature of the bioactive enzyme(s) and/or other biological active substance(s) to the textile carrier is determined by the degree of oxidation, i.e., the amount of functional group incorporated in the textile carriers.
Dialdehyde cellulose is a macromolecule with aldehyde moities randomly distributed over the chain as shown in FIG. 1 appended hereto.
The horizontal line seen in said figure represents the cellulose molecule and the vertical lines represent the aldehyde groups.
It is known in the art of enzymology engineering that the process of immobilizing large quantities of protein onto a carrier leads to steric hindrance, which can impede chemical reactions.
The ability of a carrier to capture and hold molecules such as enzymes"" and/or other bioactive substances could be expressed as a ratio between the degrees of the oxidation of the carrier to the amount of protein.
As described in GB Patent 2,240,040, the oxidation degree of a carrier varies from 0.5% (respectively 0.0625 mg.-equiv per 1 (one) gram) to 25% (3,125 mg.-equiv. per 1 gram); and the amount of immobilized enzymes varies from 0,02 per 1 (one) gram of the 0.5% oxidized carrier to 0.5 per 1 (one) gram of the 25% oxidized carrier. It is clear that a carrier with a 0.5% degree of oxidation is capable of binding 0.02% of protein, and the capability of a carrier with a 25% degree of oxidation is to bind 0.5% of protein. Thus the ratio between the oxidation degree of the carrier and the amount of protein, i.e., the ability limit of an oxidized carrier to bind molecules, such as enzymes"" or other bioactive substances"" molecules as per the GB Patent, is expressed as follows:
The Lower limit is: *0.5/0.02=25 (*respectively 0.065 mg.-equiv./gm)
The Upper Limit is: *25.0/0.5=50 (*respectively 3.125 mg.-equiv./gm)
As mentioned above, the binding nature of the enzyme(s) or other bioactive substances is determined by the concentration of aldehyde groups in a carrier. Due to the large amount of aldehyde in dialdehyde cellulose at 25% degree of oxidation, as specified in the GB publication, all the trypsin, and the enzyme(s), are bound by covalent azomethine bridges HCxe2x95x90N. The energy of an azomethine bond varies from 393 to 583 kJ/mole. The trypsin molecules in such respectively large amounts cover the Dialdehyde cellulose chain as a continuous monomolecular layer and form a shield over a significant portion of the aldehyde groups, as represented by FIG. 2 appended hereto.
It is known in the art that huge molecules of protein, (e.g., trypsinxe2x80x94a proteolytic enzymexe2x80x94has the molecular weight of 24,000 Da), inhibits and delays the functional groups of the protein and the carrier from positioning in a close proximity and thus from interacting, i.e., forming azomethine bridges. This suggests the need for a large excess of aldehydic groups over amino ones during the chemical binding of large amount of protein. Thus, the penetration, i.e., binding, of large molecules of protein such as trypsin, into an oxidized carrier and the maturation, i.e. immobilization and stabilization of the enzyme, is a slow process, which requires respectively 8-16 hours, as specified in the GB publication. During the 8-16 hours of the maturation treatment process most of the protein immobilized substance molecules are bound unevenly even randomly, covalently bound into the oxidized fabric, with a maximal concentration on top layer and a minimal below it.
Since azomethine bridges cannot be split by the wound discharge, the therapeutic effect of such dressing(s) could be attributed to the hydrolysis of dialdehyde cellulose at high oxidation levels as well as to the dissolution of oligomeric fragments of dialdehyde cellulose chain with chemically bound trypsin.
Known in the art is a method for the calculation of the hydrolysis of protein and/or other bioactive substances, incorporated in a dialdehyde cellulose carrier, as it is released from the carrier itself. According to the calculations due to the method, as per the equation of rate of release:
K[A]a[B[b[C]c . . . [Z]z . . . 
Where K is the rate constant, which is an invariable occurring of a chemical reaction, i.e. how fast the original (starting) substances disappear by hydrolysis.
[A], [B], [C] . . . [Z] . . . , stands for the current existing concentration of the reagent, and
a, b, c, . . . z . . . , are the so-called orders of the reactions.
The results are as follows:
Referring to the dressing produced according to the GB publication, from a dressing at 5% degree of oxidation and respectively 0.02% of protein covalently bound, 50% of the total amount of the protein incorporated is releasable during 36 hours, and in next 36 hours an additional 25% of the initial amount is released, i.e., during 72 hours 75% of the total amount is releasable. From a dressing of 25% degree of oxidation and respectively 0.5% of protein covalently bound, only 77% of the protein incorporated is releasable. 50% were released during the first 24 hours, and during the next 48 hours 22%-27% were released, i.e., during 72 hours 72%-77% of the initial total amount is releasable.
From the aforesaid, it will be understood that because of the dissorption process, 95%-97%, almost all of the incorporated enzyme(s) and/or another bioactive substance(s) other than enzymes, is gradually released for at least 3 (three) days.
The object of the present invention is to provide a material to be used as a dressing containing an enzyme compound and having a therapeutical effectiveness of native enzyme and prolonged action.